1. Field of Invention
This invention relates generally to a system and method for the treatment of methane emissions, and in one specific embodiment, to a system and method for the treatment of methane emissions through the use of methanotrophic microorganisms.
2. Description of the Related Art
Methane emissions, or methane off-gases, are generated by a variety of natural and human-influenced processes, including anaerobic decomposition in solid waste landfills, enteric fermentation in ruminant animals, organic solids decomposition in digesters and wastewater treatment operations, and methane leakage in fossil fuel recovery, transport, and processing systems. As a particularly potent greenhouse gas, methane emissions are responsible for about twenty percent of planetary warming, and thus represent a significant environmental concern. Accordingly, there have been numerous efforts in the past to remediate, control, and/or otherwise treat methane emissions.
In addition to processing methane that is emitted from landfills, coal mines, wastewater treatment plants, manure digesters, agricultural digesters, compost heaps, enclosed agricultural feedlots, leaking or otherwise emitting petroleum systems, several embodiments of the present invention are directed to capturing and processing methane emitted by ruminant animals. Methane emissions from ruminant animals account for about twenty percent of total global methane emissions, and atmospheric methane accounts for about twenty percent of planetary warming. In addition to the environmentally destructive effects of ruminant animal methane emissions, such emissions represent wasted energy, as a significant percentage of the food ruminant animals eat is lost as methane. Accordingly, there have been significant efforts in the past to reduce ruminant animal methane emissions.
Ruminant animal methane emissions or, more specifically, enteric fermentation methane emissions, originate in the four-stomach digestive tract common to all ruminant animals, which includes the rumen, a large forestomach connected to the four-stomach digestive tract. The rumen contains a host of digestive enzymes, fungi, bacterium, and protozoa, and the bulk of digestion, as well as methane production via enteric fermentation, takes place here. Not surprisingly, all prior efforts to reduce enteric fermentation methane emissions from ruminant animals, which include dairy cows, beef cattle, sheep, goats, water buffalo, and camels, have focused on modifications associated with the rumen or digestive tract.
Several methods are known for the treatment of natural and human-influenced methane emissions Used in conjunction with well-known methane emissions collection methods, such as landfill gas extraction wells/blowers and coal mine methane ventilation systems, the treatment of air containing captured methane emissions includes the use of turbines, microturbines, engines, reverse-flow reactors, fuel cells, and boilers to convert methane emissions into heat and/or electricity. Other well-known methods for the treatment of methane emissions include the conversion of methane emissions into pipeline-quality, liquefied, or compressed natural gas.
The treatment and utilization of methane off-gases for the production of fuel, heat, and/or electricity is described by a number of patents, including U.S. Pat. Nos. 5,642,630, 5,727,903, 5,842,357, 6,205,704, 6,446,385, and 6,666,027, herein incorporated by reference. U.S. Pat. No. 5,642,630 describes the use of landfill gas to produce high quality liquefied natural gas, liquefied carbon dioxide, and compressed natural gas products. U.S. Pat. No. 5,727,903 describes the use of landfill gas to create vehicle grade fuel. U.S. Pat. No. 5,842,357 describes the use of landfill gas to create high grade fuel and food-grade carbon dioxide. U.S. Pat. Nos. 6,205,704 and 6,446,385 describe the use of landfill gas to provide heat, electricity, and/or carbon dioxide to enhance greenhouse operations. U.S. Pat. No. 6,666,027 describes the use of off-gas from landfills and digesters to power turbines for electricity generation.
Although each of these methods is effective at treating methane emissions under a specific range of conditions, none are known to be economically and/or technologically feasible under a range of sub-optimal methane-in-air conditions, including conditions where the flow rate, concentration, or purity of methane gas emissions is variable, unpredictable, low, and/or otherwise unfavorable.
Methane-utilizing, or methanotrophic, microorganisms are well-known in the microbiology art for their capacity to grow and reproduce using methane as a source of carbon and/or energy, particularly in a wide range of diverse methane availability conditions. Accordingly, methanotrophic microorganisms have been proposed in the past as a potential tool for the remediation of methane emissions, particularly in conditions where other treatment methods are technologically and/or economically unfeasible.
Two methods have been proposed for the utilization of methanotrophic microorganisms to treat methane emissions. In one proposed process, methanotrophic microorganisms are naturally present or purposefully situated in high-methane emissions environments, such as landfill covers or coal mines, are provided with growth-stimulating nutrients, such as oxygen, water, or mineral salts, to encourage increased microbial methane emission uptake rates. This method may be carried out using nutrient injection methods such as air or water sparging to induce increased methanotrophic growth and oxidation rates in high emissions environments. U.S. Pat. No. 6,749,368, for example, describes methanotrophic microorganisms that are placed in an aerated soil cover above a municipal landfill in order to oxidize and reduce methane emissions.
In a second proposed process, air containing methane emissions is diverted into an environment containing methanotrophic microorganisms in order to cause the microbial breakdown of methane emissions. This method may be carried out by diverting air containing methane emissions into a biofiltration column containing methanotrophic microorganisms, water, and a microorganism growth medium, whereby electricity, water, nitrogen, trace minerals, and other materials are continuously added to and consumed by the system in order to effect the microbial breakdown of methane emissions.
Both of these prior methanotrophic treatment techniques cannot effectively or efficiently reduce methane emissions. Indeed, the application of these processes has been precluded in practice because while both generate continuous and costly requirements for supply-limited materials, such as electricity and minerals, neither generates direct economic benefits to recover the capital costs of treatment, and the use of methanotrophic microorganisms for the treatment of methane emissions is simply too costly to operate and sustain over time. Prior to the applicants' discovery, no methods were known to enable the practical sustainability of the biological treatment of methane emissions, and, accordingly, the utilization of methanotrophic microorganisms for the treatment of methane emissions has been precluded in practice.
Accordingly, there exists a significant need to develop a system that enables methanotrophic methane emissions treatment to be technologically, financially, and logistically sustainable and, thus, viable in practice